Array.prototype.shift()

{{JSRef}}

The shift() method of {{jsxref("Array")}} instances removes the first element from an array and returns that removed element. This method changes the length of the array.

{{InteractiveExample("JavaScript Demo: Array.shift()")}}

const array1 = [1, 2, 3];

const firstElement = array1.shift();

console.log(array1);
// Expected output: Array [2, 3]

console.log(firstElement);
// Expected output: 1

Syntax

shift()

Parameters

None.

Return value

The removed element from the array; {{jsxref("undefined")}} if the array is empty.

Description

The shift() method shifts all values to the left by 1 and decrements the length by 1, resulting in the first element being removed. If the {{jsxref("Array/length", "length")}} property is 0, {{jsxref("undefined")}} is returned.

The {{jsxref("Array/pop", "pop()")}} method has similar behavior to shift(), but applied to the last element in an array.

The shift() method is a mutating method. It changes the length and the content of this. In case you want the value of this to be the same, but return a new array with the first element removed, you can use arr.slice(1) instead.

The shift() method is generic. It only expects the this value to have a length property and integer-keyed properties. Although strings are also array-like, this method is not suitable to be applied on them, as strings are immutable.

Examples

Removing an element from an array

The following code displays the myFish array before and after removing its first element. It also displays the removed element:

const myFish = ["angel", "clown", "mandarin", "surgeon"];

console.log("myFish before:", myFish);
// myFish before: ['angel', 'clown', 'mandarin', 'surgeon']

const shifted = myFish.shift();

console.log("myFish after:", myFish);
// myFish after: ['clown', 'mandarin', 'surgeon']

console.log("Removed this element:", shifted);
// Removed this element: angel

Using shift() method in while loop

The shift() method is often used in condition inside while loop. In the following example every iteration will remove the next element from an array, until it is empty:

const names = ["Andrew", "Tyrone", "Paul", "Maria", "Gayatri"];

while (typeof (i = names.shift()) !== "undefined") {
  console.log(i);
}
// Andrew, Tyrone, Paul, Maria, Gayatri

Calling shift() on non-array objects

The shift() method reads the length property of this. If the normalized length is 0, length is set to 0 again (whereas it may be negative or undefined before). Otherwise, the property at 0 is returned, and the rest of the properties are shifted left by one. The property at length - 1 is deleted, and the length property is decremented by one.

const arrayLike = {
  length: 3,
  unrelated: "foo",
  2: 4,
};
console.log(Array.prototype.shift.call(arrayLike));
// undefined, because it is an empty slot
console.log(arrayLike);
// { '1': 4, length: 2, unrelated: 'foo' }

const plainObj = {};
// There's no length property, so the length is 0
Array.prototype.shift.call(plainObj);
console.log(plainObj);
// { length: 0 }

Specifications

{{Specifications}}

Browser compatibility

{{Compat}}

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